Hakan Giir, MD, PhD, Bedrettin Akova, MD, Selfuk Kiifiiko~lu, MD

Transcription

1 1024 Continuous Versus Separate Isokinetic Test Protocol: The Effect of Estradiol on the Reproducibility of Concentric and Eccentric Isokinetic Measurements in Knee Muscles Hakan Giir, MD, PhD, Bedrettin Akova, MD, Selfuk Kiifiiko~lu, MD ABSTRACT. Gtir H, Akova B, Ktigtiko~lu S. Continuous versus separate isokinetic test protocol: the effect of estradiol on the reproducibility of concentric and eccentric isokinetic measurements in knee muscles. Arch Phys Med Rehabil 1999;80: Objective: To investigate the effects of estradiol on the reliability of concentric and eccentric isokinetic measurements of knee muscles and to compare the reproducibility of measurements in a continuous test protocol and a separate test protocol. Design: Repeated measurements. Setting: A university exercise physiology laboratory. Participants: Twenty healthy sedentary women volunteers, aged 19 to 37 years, who had regular menstrual cycles (ranging from 27 to 35 days). Subjects were randomly divided into two groups: continuous test group (n = 10) and separate test group (n = 10) and tested at the menstrual phase (days 1 to 3) and preovulatory phase (days 12 to 14) in both legs. Methods: Continuous reciprocal flexion-extension contractions were used in the continuous test group, and separated flexion and extension contractions were used in the separate test group. Four different test protocols were designed to determine the effects of test mode and number of contractions on the isokinetic measurements: Group A, 4 reciprocal flexionextension repetitions at each angular velocity of 60 /sec and 180 /sec in one leg in the continuous test group; Group B, 4 and 20 reciprocal flexion-extension repetitions at 60 /sec and 180 /sec, respectively, in the contralateral leg in the same group; Group C, 4 repetitions in extensors and flexors at each angular velocity of 60 /sec and 180 /sec with a 5-minute rest between the two muscle groups in one leg in the separate test group; and Group D, 4 repetitions at 60 /sec and 20 repetitions at 180 /sec for extensors and flexors with a 5-minute rest between the two muscle groups in the contralateral leg in the same group. Blood samples were analyzed for sex hormones, creatine kinase, and lactate dehydrogenase before the tests at the menstrual phase and the preovulatory phase. In addition subjective assessment of muscle soreness was made at each blood sampling. Results: Concentric and eccentric peak torque, average power, total work, and endurance ratio at both angular velocities were not significantly different in the two phases of the cycle by paired observation t test for each of the four groups. Except for concentric and eccentric endurance ratios of quadriceps and hamstrings, and concentric peak torque and average power of hamstrings at 180 /sec in Group D, intraclass Prom the Department of Sports Medicine, Medical School of Uluda~ University, Bursa, Turkey. Submitted for publication May 5, Accepted in revised form November 20, The authors have chosen not to select a disclosure statement. Reprint requests to Hakan Giir, MD, Department of Sports Medicine, Medical School of Uluda~ University, Bursa, Turkey by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /99/ /0 correlation coefficients of tested variables showed correlations that were moderate to excellent (p <.05) between two phases. In addition, there were no significant correlations between estradiol and the tested variables. Resting serum creatine kinase and lactate dehydrogenase activities and the score of muscle soreness were at the baseline and not significantly different prior to the tests performed at preovulatory and menstrual phases. Conclusions: The results suggest that: (1) reproducibility of isokinetic tests during the menstrual cycle is not influenced by sex hormone fluctuations, particularly estradiol; (2) when compared with the separate test protocol used in this study, the continuous test protocol is more appropriate to measure peak torque, average power, total work, and endurance ratio for both muscle groups of the knee even if the number of contractions is changed. However, these conclusions are specific to sedentary individuals; to make more valid conclusions, further studies with different subject groups are needed by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation "1~ ELIABILITY OF ISOKINETIC test measurements has l'loften interested investigators attempting to select the best testing protocols. The reliability of concentric and eccentric tests for knee extensors (quadriceps) and flexors (hamstrings) has been investigated using different devices, protocols, and angular velocities. 1-6 In these studies intraclass correlation coefficients of peak torque, total work, and average power were reported to be moderate to excellent for test-retest reliability. 2 Kramer and colleagues also reported that intraclass correlation coefficients were slightly higher for men than for women and concluded that this could be related to activity levels. Women with regular menstrual cycles, however, also have large variations in levels of sex hormones, particularly estradiol, which could be related to muscular performance and metabolic action during muscular exercises. 7"1 11 In a previous study, we tested concentric and eccentric peak torque and total work of quadriceps and hamstrings at angular velocities of 60 /sec (4 repetitions) and 180 /sec (20 repetitions) in the menstrual, follicular, and luteal phases. We found that the test-retest reliabilities of the two peak torques and total work were moderate to excellent during the menstrual cycle. 11 However, intraclass correlation coefficients were very low for concentric peak torque and total work of knee flexors performing 20 continuous reciprocal flexion/extension repetitions of maximal voluntary contractions at an angular velocity of 180 /sec. Therefore, we conclude that a continuous protocol that involves several repetitions of contractions may not be an appropriate test protocol to measure peak torque and total work, particularly for sedentary individuals, probably because of fatigue. Consequently, we believe that the effect of the number of repetitions and the effect of a continuous test protocol on the reliability of peak torque and total work measurements should be better explained.

2 ISOKINETIC MEASUREMENTS DURING MENSTRUAL CYCLE, Gfir 1025 The effects of continuous bidirectional and intermittent unidirectional modes of muscular contraction on isokinetic concentric peak torque of knee extension and flexion were investigated by Gleeson and associates. 12 Although they suggested that both contraction modes might be used with equal effectiveness to assess isokinetic leg strength characteristics, they found significantly greater scores for bidirectional than for unidirectional flexion peak torque at 180 /sec. They also reported that bidirectional contractions may offer increased torque outputs during contractions of the knee flexor muscles. In their study, however, they only evaluated concentric peak torque of knee extensors and flexors in adult men. From a literature search, it appears that there are no reported studies comparing the effects of continuous and separate test modes on the reliability of concentric and eccentric average power, total work, and endurance ratio, or eccentric peak torque of quadriceps and hamstrings, nor are there studies that describe the effects of sex hormones on these measurements. The questions that arose following our previous study and the lack of information in the literature led us to investigate (1) the effects of estradiol, (2) the effects of the number of contractions, and (3) the effects of continuous (reciprocal) and separate modes of muscular contraction on the reliability of isokinetic concentric and eccentric measurements of knee muscles in sedentary individuals during the menstrual cycle. The two different phases of the cycle in which estradiol levels are respectively highest and lowest, preovulation and menses, were chosen according to previous observations on the effects of estradiol on muscular performance. 7-1 Muscular damage and soreness following eccentric muscular work have been reported by several investigators. I3,14 It was reported that muscle adaptation and recovery after eccentric exercise takes at least 1 to 2 weeks. 15,16 Moreover, Tiidus 17 suggested that there was less exercise-induced oxidative stress and muscle membrane disruption in female rats than in male rats because of the antioxidant and membrane stabilizing properties of estrogens. In most of the previous studies ~6 on the reliability of isokinetic concentric and eccentric measurements, however, investigators generally used 3- to 7-day intervals for test-retest, whether or not they used female subjects. Therefore, to assess muscle adaptation and recovery associated with estradiol from the first test to the second test, we measured serum creatine kinase (CK) and lactate dehydrogenase (LDH) levels together with muscle soreness. MATERIAL AND METHODS Subjects Twenty sedentary women aged 19 to 37 years with normal menstrual cycles who did not take any oral contraceptive drugs volunteered as study subjects. They completed a questionnaire on menstrual status, to determine cycle regularity, and were included in the study if their menstrual status was regular for three consecutive cycles and the average time of menses was between 27 and 35 days. All volunteers had a medical examination (cardiovascular, respiratory, musculoskeletal, etc) before the study and those without a health problem that might pose a risk during the maximal test were included in the study. The subjects had no history of musculoskeletal disease and had not undergone any orthopedic procedures that would affect their leg muscle performance. Subjects were informed about testing procedures, as well as possible risk and discomfort that might ensue, and gave their written informed consent to participate. None of the subjects had engaged regularly in leisure-time physical activity such as walking, running, swimming, or other exercise in the previous 10 years. All subjects worked in offices, with much of their day spent sitting. Therefore, all subjects were at Level I according to activity levels (for both occupational and leisure-time activities) as defined by Saltin and Grimby.18 The activity level for all subjects remained relatively constant during the experimental period. Testing Order The tests were carried out during the menstrual phase (days 1 to 3) and the preovulatory phase (days 12 to 16) at the same time of the day. Thus, there were 12- to 16-day intervals between testing occasions for recovery of the muscles. Testing order was randomized for subjects during two consecutive menstrual cycles, such as preovulatory-menstrual and menstmalpreovulatory, to minimize the effects of fatigue and adaptation to procedures and the device. The exact time of the phases was determined by sex hormone levels. In addition, estimated cycle phases were subsequently verified by measurements of plasma ovarian hormones. Isokinetic Tests All tests were completed on a Cybex 6000 a computercontrolled isokinetic dynamometer, which was calibrated before every test session. Subjects were positioned sitting with the backrest at a 90 angle and were instructed to grip the sides of the seat during the testing. The thigh, pelvis, and trunk were stabilized with straps. An adjustable lever arm was attached to the leg by a padded cuff just proximal to the lateral malleolus. The axis of rotation of the dynamometer arm was positioned just proximal to the lateral femoral epicondyle. Gravity corrections to torque at 45 (0 = straight leg) were calculated by the computer software. Subjects were randomly divided into two groups: the continuous test group (n = 10) and the separate test group (n -- 10). Conventional concentric and eccentric continuous (reciprocal) isokinetic tests were used in the continuous test group. During the tests the subjects in this group performed 4 maximal reciprocal flexion-extension repetitions at each angular velocity of 60 /sec and 180 /sec in one leg, while performing 4 and 20 maximal reciprocal flexion-extension repetitions at 60 /sec and 180 /sec, respectively, in the contralateral leg. A 20-minute rest was allowed between the tests, and for each leg. For the separate test group, we used a continuous passive motion mode. During the concentric test, while the lever arm of the device moved passively in both directions of flexion and extension, for the measurement of knee extensors the subjects extended their legs into an upstroke as vigorously and as fast as possible and did not make any effort while their legs were moved down passively by the lever arm. After a 5-minute rest period, for the measurement of flexors the subjects pulled their legs into a downstroke as vigorously and as fast as possible and did not make any effort while their legs were moved up passively by the lever arm. After a 20-minute rest following concentric measurements, eccentric extensors were measured in the separate test group as follows: while the lever arm was moved down by the device the subjects resisted against the calf pad as vigorously and as fast as possible and then passively let their legs be moved up by the lever arm. After a 5-minute rest, flexors were measured as follows: while the lever arm moved up the subjects resisted against the calf pad as vigorously and as fast as possible and let their legs be passively moved down by the lever arm. For both measurements in this group, the subjects performed 4 maximal repetitions at each angular velocity of 60 /sec and 180 /sec in one leg and 4 and 20 maximal repetitions at 60 /sec and 180 /sec, respectively, in the contralateral leg. A 20-minute rest was also given for both legs. Finally, four different test protocols were designed as follows.

3 1026 ISOKINETIC MEASUREMENTS DURING MENSTRUAL CYCLE, GLir Group A: In the continuous test group, 4 reciprocal flexionextension repetitions at each angular velocity of 60 /sec and 180 /sec in one leg. Group B: In the continuous test group, 4 and 20 reciprocal flexion-extension repetitions at 60 /sec and 180 /sec, respectively, in the contralateral leg. Group C: In the separate test group, 4 repetitions in extensors and flexors at each angular velocity of 60 /sec and 180 /sec with a 5-minute rest between the two muscle groups in one leg. Group D: In the separate test group, 4 repetitions at 60 /sec and 20 repetitions at 180 /sec for extensors and flexors with a 5-minute rest between the two muscle groups in the contralateral leg. These test protocols were chosen to investigate the effect of both number and mode (reciprocal and separate) of contractions on the isokinetic concentric and eccentric measurements of knee muscles during the menstrual cycle. The order of speed was from slower to faster as suggested by Wilhite and colleagues. 4 A 20-second rest was allowed between each contraction speed. The knee moved through the whole range of motion between 10 and 90 (0 = straight leg) during the tests, and subjects were verbally encouraged by the same individual who administered the tests to produce maximal efforts. The subjects, inexperienced in the use of the isokinetic dynamometer, were familiarized with testing procedures by performing three consecutive submaximal warm-up trials for each muscle group and speed, one of which was a maximal contraction as recommended by Snow and Blacklin. 5 After a 20-second rest period, peak torque, average power, total work, and endurance ratio of knee extensor and flexor muscle groups were measured by maximal voluntary contractions. Endurance ratio, which is calculated by dividing the work done in the last 50% of the set by the work done in the first 50% of the set, was measured only in Groups B and D, where we used 20 repetitions of contractions at 180 /sec. Eccentric tests were performed after concentric tests since Komi 19 has reported that greater force is produced in a concentric contraction preceded by an eccentric contraction than by a concentric contraction performed alone, because muscle elastic potential energy improves after eccentric contractions. Repeated isokinetic tests in the preovulatory and menstrual phases were performed on the same legs of subjects. Analyses of Blood Samples Blood was sampled between 8 and 10 AM on the day of the tests performed for preovulatory and menstrual phases. Estradiol, progesterone, follicle stimulating hormone, and luteinizing hormone concentrations in serum were measured by radio immunoassay techniques using commercial kits of Amerilite Assay. b Total and free testosterone concentrations in serum were also measured by radioimmunoassay techniques using a commercial kit of DPC. c Serum CK and LDH activities were measured by Dax 72 d using Technicon d test kits and methods. Subjective assessments of muscle soreness were made at each blood sampling. Soreness was scored on a scale of 1 (normal) to 10 (very, very sore) for both extensor and flexor muscle groups. Statistics Standard procedure was used to calculate mean ± standard deviation. To compare the data in the two phases, paired observation t test was used. In each case the significant level was set at p <.05. The intraclass correlation coefficients (1,1) were calculated for isokinetic data to determine the reproducibility of concentric and eccentric tests between two occasions. 2 The data of each of 4 groups measured at the two phases (n = 20) were pooled and stepwise regression analyses performed between estradiol and selected test variables. A correlation of at least r > was required to obtain statistical significance at the p <.05. Subjects. RESULTS In the continuous test group, the mean age was years, mean height was cm, and the mean menstrual cycle length was days. In the separate test group, mean age was years, mean height was cm, and mean menstrual cycle length was days. The body weight of continuous test group subjects was kg in the menstrual phase and kg in the preovulatory phase. In separate test group subjects, body weight was kg in the menstrual phase and _ 5.5kg in the preovulatory phase. Differences in age, body weight, and height were not statistically significant between the two groups, nor was body weight significantly different between the menstrual and preovulatory phases. Hormones. Mean values of serum hormone levels were different in the menstrual and preovulatory phases, but only estradiol and leuteinizing hormone levels were significantly higher (p <.05) during the preovulatory phase (table 1). There was no significant correlation between estradiol and tested variables by stepwise regression analyses. Muscle recovery and soreness. Serum CK and LDH levels in the separate test group were and U/L before the preovulating phase tests and and U/L before the menstrual phase tests. In the continuous test group, the serum CK level was U/L and the LDH level was U/L before the preovulating phase tests; before the menstrual phase tests the serum CK level was U/L and the LDH level was U/L. The differences between the preovulating phase and the menstrual phase were not statistically significant. Muscle soreness, on a scale of 1 to 10, was scored as 1 (normal) by all subjects before isokinetic tests at both phases. Table 1: Plasma Hormone Levels of Subjects at Menstrual and Preovulatory Phases Continuous Sepa rate (n = 10) (n = 10) Hormones Menstrual Preovulatory Menstrual Preovulatory Follicle-stimulating hormone (U/L) Luteinizing hormone (U/L) Estradiol (pg/ml) Progesterone (ng/ml) Total testosterone (ng/ml) Free testosterone (ng/ml) 4.1 _ ,4 +_ _ _ _ " 3.7 _ , * _ _+ 79.2* _ , * 0.7 _ _ _ _ _ _ ± _ _ 1.5 Values reported as mean --- standard deviation. * p <.05 between menstrual and preovulatory phases.

4 ISOKINETIC MEASUREMENTS DURING MENSTRUAL CYCLE, GLir 1027 Table 2: Intraclass Correlation Coefficients (Relative Differences in Mean Values) Between Preovulatory and Menstrual Phases for Concentric and Eccentric Continuous Versus Separate Tests of Quadriceps Angular Continuous Separate Velocity Group A Group B Group C Group D ( /see) r(%) r(%) r(%) r(%) Concentric (2.8).79 (2.7).94 (4.3).99 (1.7) (1.5).85 (1.4).98 (4,0).96 (2.6) (2.9).79 (2.5).96 (5,4).89 (5.4) (6.8).62 (9.5).78 (2,4).72 (3.9) (2.1).81 (4.0).97 (3.0).99 (2.0) (1.6).79 (0.0).96 (4.8).94 (1.5) ER (0.0).19 (1.3) Eccentric (0.0).81 (3.4).85 (1.1).87 (1.8) (4.0).82 (1.3).90 (2.8).85 (5,6) (5.1).85 (8.6).71 (2.8),59 (6.3) (3.0).82 (2.8),63 (1.1).65 (10,5) (3.9).82 (4.1).85 (3.5).93 (0.0) (6.4).87 (0.0).89 (0.7).79 (10.1) ER (10.1).10 (10.4) For r- >.55, p <.05. Abbreviations:, peak torque;, average power; ER, endurance ratio;, total work. Reliability of concentric and eccentric tests. Concentric and eccentric peak torque, average power, total work, and endurance ratio at both angular velocities were not significantly different in the two phases of the cycle by paired observation t test for either group and for subgroups of low or high number of repetitions. There were no statistical differences between the two phases for the peak torque, average power, and total work relative to body weight since subjects gained no extra weight during the menstrual cycle. Intraclass correlation coefficients of tested variables of quadriceps and hamstrings at the two angular velocities are summarized in tables 2 and 3, respectively. Table 3: Intraclass Correlation Coefficients (Relative Differences in Mean Values) Between Preovulatory and Menstrual Phases for Concentric and Eccentric Continuous Versus Separate Tests of Hamstring Concentric ER Eccentric ER Angular Continuous Separate Velocity Group A Group B Group C Group D ( /see) r(%) r(%) r(%) r(%) (8,0).85 (0,0).97 (3.1).72 (4.2) (4.4).78 (8.4).94 (7.5),23 (5.2) (2.3).89 (2.2).74 (6.8).69 (5.4) (2.8).66 (5.5).85 (0,0),15 (3.9) 60,86 (4.9),91 (0.0).94 (0.0).64 (2.0) 180,90 (5.4).67 (4.8).97 (4.5).92 (1.5) (9.5).32 (1,3) (4.5).77 (0.0).89 (0.0).68 (2.9) (4.3).80 (3,1).94 (0.0).87 (1.9) (10.0).76 (4.4).59 (9.5).90 (7.6) (4.1).64 (7.4).63 (2.4).70 (10.6) (1.2).76 (4.9).94 (0.0).79 (1.2) (7.5).76 (3.6).88 (1.2).89 (2.3) (2,1),50 (5.4) For r- >.55, p<.05. Abbreviations:, peak torque;, average power; ER, endurance ratio;, total work. Except for the endurance ratio in Group D of the separate test group for quadriceps and hamstrings, all variables showed moderate to excellent correlations (p <.05). However, intraclass correlation coefficients of the endurance ratios of quadriceps and hamstrings were good and moderate, respectively, in Group B of the continuous test group. In addition, there were poor correlations between the two phases for concentric peak torque and average power of hamstrings at 180 /see in Group D of the separate test group, where 20 repetitions were used (table 3). The relative differences in mean values of tested variables were in the range of 0% to 9.5% and 0% to 10.5% for concentric and eccentric tests in quadriceps, respectively, and were in the range of 0% to 9.5% and 0% to 10.6% for concentric and eccentric tests in hamstrings, respectively (tables 2 and 3). The average intraclass correlation coefficients for peak torque, average power, and total work for quadriceps concentric and eccentric tests, respectively, were.93 and.81 in Group A,.78 and.83 in Group B,.93 and.81 in Group C, and.92 and.78 in Group D. Similarly, for hamstrings concentric and eccentric tests, respectively, they were.90 and.87 in Group A,.79 and.75 in Group B, and.90 and.81 in Group C. The average intraclass correlation coefficient of hamstrings in Group D was.81 for eccentric tests and.56 for concentric tests. DISCUSSION This study's findings indicate that the mean values of concentric and eccentric peak torque, average power, total work, and endurance ratio are not influenced by sex hormones, particularly estradiol, in sedentary individuals, as reported by several investigatorsj 1,zv23 In addition, intraclass correlation coefficients for test-retest during the menstrual cycle were moderate to excellent for concentric mad eccentric measurements of quadriceps, both in continuous and separate test protocols. This was true even if the number of contractions was changed, with the exception of concentric and eccentric endurance ratios in the separate test protocol. Intraclass correlation coefficients for test-retest of both measurements of hamstrings also demonstrated moderate to excellent correlations in the continuous protocol for both low and high numbers of repetitions. However, the coefficients for concentric peak torque and average power at an angular velocity of 180 /see, where 20 repetitions were used, were poor in the separate protocol. Moreover, the data showed that 12- to 16-day intervals are enough for muscle adaptation and recovery for repeated isokinetic tests. The test protocol used in our previous study, 11 which included continuous reciprocal contractions at angular velocities of 60 /see (4 repetitions) and 180 /see (20 repetitions), is similar to the test protocol for Group B in the present study. In our previous study, the highest and lowest serum estradiol levels, respectively, were found in the luteal and menstrual phases. Therefore, these phases seem to provide the most suitable data to compare and discuss the results of the present study. Intraclass correlation coefficients of concentric and eccentric tests of quadriceps in Group B were similar in both of our studies. Peak torque was.81 in the present study and.87 in the earlier study; total work was.83 in this study and.84 in the other study. The average intraclass correlation coefficients in the hamstrings were.77 for concentric tests and.78 for eccentric tests in the present study and.43 and.74, respectively, in the earlier study. Although the same test protocols were used, the subjects were tested three times with 5- to ll-day intervals in the earlier study, whereas subjects in this study were tested twice with 12- to 16-day intervals. Subjects in the previous study may have been fatigued, which

5 1028 ISOKINETIC MEASUREMENTS DURING MENSTRUAL CYCLE, G(ir could be the reason for the difference in hamstrings' coefficients. Ebbeling and Clarkson 16 investigated the effects of performing a second eccentric exercise bout before and after recovery from the first bout. In their study one group of subjects performed the second bouts of eccentric exercise on the fifth day after the first bout; a second group did the second exercises on the 14th day. They found that the subjects regained only 66% and 87% of initial strength at the second bouts performed on days 5 and 14, respectively; the average works performed at the second bouts were 87% and 99% of initial work for days 5 and 14, respectively. The scores of delayed-onset muscle soreness, which had a peak on days 2 to 3 following the first bout with a score of 5 to 6, declined with scores of 2 to 3 and 1 to 2 before the second bout on days 5 and 14, respectively. In addition, while the serum CK level returned to baseline before the 14th-day second bout, it was still very high prior to the fifth-day second bout. These results suggest that the process of recovery after an exercise inducing muscle damage is slow, and more than one week for recovery is necessary to have full muscle function after the initial bout. The results of muscle soreness and selected products of muscle damage that were found at the baseline level before testing in the present study could also support that idea about the effects of fatigue. Further studies, with different subject groups and muscle groups, are needed to clarify the recovery process for repeated isokinetic measurements. The effects of the menstrual cycle on isokinetic measurements were also investigated by Dibrezzo and associates, 21 who examined isokinetic concentric peak torque and endurance at three speeds (60, 180, and 240 /sec) during the menses (within 24 hours of onset), ovulation (13 to 14 days from onset), and luteal phase (10 days from ovulation). They found that correlation coefficients for concentric peak torques of flexors and extensors were.64 and.76, respectively, at 60 /sec and.74 and.89, respectively, at 180 /sec for the ovulatory and menstrual phases, whereas correlation coefficients for concentric endurance ratios were.69 and.76 in flexors and extensors, respectively, at 240 /sec. Our intraclass correlation coefficients were greater for peak torque at 60 and 180 /sec than were those found by Dibrezzo, who used a similar test protocol (same speeds and number of repetitions) in the same phases. However, Dibrezzo tested subjects three times during the menstrual cycle, which might have restricted the recovery time for the muscles. Therefore, the test protocol used by Dibrezzo possibly did not offer an adequate rest period. In addition, their order of test speeds (60, 180, and 240 /sec) varied at different cycle phases, whereas in our study the order always was from slower to faster. This might be another reason for the differences in the results of two studies, since applying the test speeds in different orders has been reported to influence the degree of reliability. 4 One reason for different intraclass correlation coefficients in the two studies might be the difference in the activity levels of subjects, since Dibrezzo's subjects were fairly active participants. Moreover, Dibrezzo defined cycle phases by counting days in the study, rather than determining serum hormone levels as we did. Therefore, the differences between the two studies hinder an accurate comparison of the results. Also, although the test speeds (240 /sec in the Dibrezzo study and 180 /sec in the present study) and the method for calculating endurance ratio (first four to last four in Dibrezzo and first 50% to last 50% in our study) are different, coefficients for concentric extensors and flexors were similar, with values of.76 and.69, respectively, in Dibrezzo and.72 and.77, respectively, in our study. Because Dibrezzo did not perform eccentric tests, the comparison between the two studies is limited to concentric tests. When continuous tests (Groups A and B) were compared with separate tests (Groups C and D) in terms of the reproducibility of selected test parameters other than endurance ratio, there was not a remarkable difference in intraclass correlation coefficients for concentric and eccentric isokinetic indices of quadriceps. However, the coefficients for concentric peak torque and average power in Group D at 180 /sec, where 20 contractions were used, were poor for hamstrings. Moreover, better reliability was found for concentric and eccentric endurance ratio of quadriceps and hamstrings in the continuous test group than in the separate test group. It is possible to conclude that the continuous reciprocal isokinetic test mode may be preferable to the separate isokinetic test mode to evaluate isokinetic strength indices in knee muscles during the menstrual cycle. A similar suggestion was made by Gleeson and coworkers, 12 who examined the effects of continuous bidirectional and intermittent unidirectional contractions of knee extensors and flexors on concentric peak torque in adult men. Gleeson 12 also reported that bidirectional contractions may generate increased torque outputs during contractions of the knee flexor muscles than are generated by intermittent unidirectional contractions. Since we used different subjects in the continuous and separate test groups, it is impossible to compare the data obtained from the continuous test with the data obtained from the separate test. Moreover, the intraclass correlation coefficient for peak torque of hamstrings was excellent in the present study in Group C, which had the same speed (180 /sec) and number of contractions (4) as used by Gleeson. 12 In another study, Bohannon and colleagues 24 tested the effect of resisted and passive knee flexion on subsequent peak knee extension torque at angular velocities of 60 /sec and 120 /sec in healthy, untrained adult women and men. The subjects performed reciprocally I0 maximal voluntary knee extensions following either passive or maximal voluntary resisted knee flexion identical to the continuous and separated test modes we used. Bohannon 24 could not find any significant difference between the peak knee extension torque produced in the two knee flexion conditions at any speeds. Because both Gleeson 12 and Bohannon z4 tested merely peak torque value in their studies, our discussion is limited to peak torque. Some differences in our results and those of Gleeson and Bohannon might be related to the differences in the number of contractions, testing speeds, and mode used. Despite differences in methods, the results of Gleeson and Bohannon support our findings that the continuous test mode may be preferable to the separate test mode for reproducibility of concentric isokinetic measurements. There are no eccentric data in the Gleeson and Bohannon studies to make a similar suggestion for eccentric isokinetic measurements. Bohannon 25 found that the mean peak torque of extension during repeated extensionflexion reversals was 5% greater than the mean peak torque extension during separated knee extension-flexion dyads in hemiparetic patients at 60 /sec of angular velocity. Further investigation, particularly with different subject groups, is needed to make valid conclusions on the reliability of the separate test protocol we used. CONCLUSION This study showed that: (1) sex hormone fluctuations, particularly estradiol, had no influence on reproducibility of isokinetic tests during the menstrual cycle; (2) in contrast to our previous work, the conventional continuous reciprocal flexionextension test protocol is an appropriate test protocol for repeated test measurements of hamstrings to determine peak torque, average power, total work, and endurance ratio; and (3) the separate test protocol used in this study, which involved a high number of repetitions of contractions, is not optimal.

6 ISOKINETIC MEASUREMENTS DURING MENSTRUAL CYCLE, Gfir 1029 These conclusions, however, should be generalized only to sedentary women between the ages of 19 and 37 years; to make more valid conclusions, further studies with different subject groups are needed. In addition, the time interval between isokinetic test-retest could be important for the muscle recovery and adaptation, particularly after eccentric contractions, to obtain better results of isokinetic measurements in sedentary individuals. References 1. Tredinnick TJ, Duncan PW. Reliability of measurements of concentric and eccentric isokinetic loading. Phys Ther 1988;68: Kramer JF. Reliability of knee extensor and flexor torques during continuous concentric-eccentric cycles. Arch Phys Med Rehabil 1990;71: Steiner LA, Harris BA, Krebs DE. Reliability of eccentric isokinetic knee flexion and extension measurements. Arch Phys Med Rehabil 1993;74: Wilhite MR, Cohen ER, Wilhite SC. Reliability of concentric and eccentric measurements of quadriceps performance using the Kin-Corn dynamometer: the effect of testing order for three different speeds. J Orthop Sports Phys Ther 1992; 15: Snow C J, Blacklin K. Reliability of knee flexor peak torque measurements from a standardized test protocol on a Kin/Corn dynamometer. Arch Phys Med Rehabil 1992;73: Wessel J, Gray G, Luongo F, Isherwood L. Reliability of work measurements recorded during concentric and eccentric contractions of the knee extensors in healthy subjects. Physiother Can 1989;41: Bunt JC. Metabolic actions of estradiol: significance for acute and chronic exercise response. Med Sci Sports Exerc 1990;22: Rice PL Relationship of estrogen to strength, percent body fat and oxygen uptake in women. J Sports Med 1988;28: Petrofsky JS, Ledonne DM, Rinehart JS, Lind AR. Isometric strength and endurance during the menstrual cycle. Eur J Appl Physiol 1976;35: Wirth JC, Lohman TG. The relationship of static muscle function to use of oral contraceptives. Med Sci Sports Exerc 1982; 14: Gtir H. Concentric and eccentric isokinetic measurements in knee muscles during the menstrual cycle: a special reference to reciprocal moment ratios. Arch Phys Med Rehabil 1997;78: Gleeson NP, Parry A, Mercer TH. The effect of contraction mode on isokinetic leg strength and associated day-today reproducibility in adult males. J Sports Sci 1994;12: Maughan RJ, Donnely AE, Gleeson M, Whiting PH, Walker MKA, Clough PJ. Delayed-onset muscle damage and lipid peroxidation in man after a downhill run. Muscle Nerve 1989; 12: I4. Schwane J, Johnson SR, Vandenakker CB, Armstrong RB. Delayedonset muscle soreness and plasma CPK and LDH activities after downhill running. Med Sci Sports Exerc 1983;15: Clarkson PM, Tremblay I. Exercise-induced muscle damage, repair and adaptation in humans. JAppl Physiol 1988;65: Ebbeling CB, Clarkson PM. Muscle adaptation prior to recovery following eccentric exercise. Eur J Appl Physiol 1990;60: Tiidus PM. Can estrogens diminish exercise induced muscle damage? Can J Appl Physiol 1995;20: Saltin B, Grimby G. Physiological analysis of middle aged and old former athletes. Circulation 1968 ;38: Komi PV. The stretch-shortening cycle and human power output. In: Jones NL, McCartney N, McComas AJ, editors. Human muscle power. Champaign (IL): Human Kinetics; p Strout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86: Dibrezzo R, Fort IL, Brown B. Relationships among strength, endurance, weight and body fat during three phases of the menstrual cycle. J Sports Med Phys Fitness 1991 ;31: Lebmn CM, McKenzie DC, Prior JC, Taunton IE. Effects of menstrual cycle phase on athletic performance: Med Sci Sports Exerc 1995;27: Lebrun CM. Effect of the different phases of the menstrual cycle and oral contraceptives on athletic performance. Sports Med 1993; 16: Bohannon RW, Gibson DF, Larkin R Effect of resisted knee flexion on knee extension torque. Phys Ther 1986;66: Bohannon RW. Knee extension torque during repeated knee extension-flexion reversals and separated knee extension-flexion dyads. Phys Ther 1985;65:1052-4, Suppliers a. Lumex Inc., 2100 Smithtown Avenue, Ronkoma, NY b. Kodak Diagnostic GmbH, D-3300, Braunschweing, Germany. c. Diagnostic Products Corporation, 5700 West 96th Street, Los Angeles, CA d. Technicon Instruments Corporation, Tarrytown, NY.